Magnetron device

ABSTRACT

A magnetron device, wherein a shield box is disposed on that side of a magnetron tube which faces a cathode stem; the shield box contains a choking system for preventing the leakage of microwave energy; and the choking system is formed of a pair of choking members, each of which has first and second choking elements, the first choking element being composed of a coil connected to a filament lead conductor and a high frequency core of high intrinsic resistivity received in the coil, and the second choking element being composed of a coil connected to the coil of the first choking element and a low frequency core of low intrinsic resistivity received in the second choking element coil.

United States Patent Tashiro Nov. 25, 1975 [54] MAGNETRON DEVICE 3,727,098 4/1973 Crabuchettes 331/86 x 6 7 l974 d 3 5/3 .53 [75] Inventor: Norio Tashiro, Yokohama, Japan H/ Him a 1 9 [73] Assignee: Tokyo Shibaura Electric (10., Ltd., primary E i A]f d L. Brody Kawasaki, Japan Attorney, Agent, or FirmOblon, Fisher, Spivak, 221 Filed; on. 24, 1974 Mcclelland & Male [Zl] Appl. No: 517,613

[57] ABSTRACT [30] Foreign Application Priority D t A magnetron device, wherein a shield box is disposed Nov 12 i973 Japan i. 48-12709) that Side of a magnetron which faces a ode stem; the shield box contains a choking system for PI'CVEfltil'lg the leakage Of microwave energy; and the 315/395]. 315/85v 331/86 choking system is formed of a pair of choking mem [51] Int u H0 29/76; HB 9/02. bers, each of which has first and second choking ele- HOU ZS/SO. H01] ments, the first choking element being composed of a [58] Field of Sekrch 328/227 5/3951 coil connected to a filament lead conductor and a high 315/3953 39] 331/5 frequency core of high intrinsic resistivity received in 219/1055 R 055,8 1055 the coil, and the second choking element being com posed of a coil connected to the coil of the first chok- [56] References Cited ing element and a low frequency core of low intrinsic UNITED STATES PATENTS resistivity received in the second choking element coil 3.68l,652 8/l972 Domenichini et al. 315/85 Claims, 12 Drawing Figures q "60 200 I 2K] c l 230 V" E c O 250 t f 170-1 170-2 23b 0 25b l6b b 3 24 i8b 17b-l wb-z 21b \X V\\ iTb U.S. Patent Nov. 25, 1975 Sheet2of5 3,922,612

US. Patent Nov. 25, 1975 Sheet30f5 3,922,612

US. Patent Nov. 25, 1975 Sheet 4 of5 FIG. 9

FIG. 10

US. Patent N0v.25, 1975 SheetSofS 3,922,612

FIG. H

AGC VOLTAGE (v) CHANNEL 2 MAGNETRON DEVICE This invention relates to a magnetron device and more particularly to a magnetron devicc improved in the choking circuit.

A magnetron is used incorporated in, for example, an electronic oven with its output antenna received in the closed chamber of the oven, for cooking, for example, food material by microwave energy delivered from the output antenna. When the magnetron is put into operation, a cathode bushing formed of, for example, ceramic material emits high frequency waves bearing the VHF and UHF bands. The above-mentioned type of magnetron which gives forth these high frequency waves disturbing a television receiving set is provided with a low pass filter to prevent their leakage.

A low pass filter for the prior art magnetron comprises a pair of choke coils each including a ferrite core and a capacitor penetrated by a pair of filament lead conductors. The cathode section of the prior art magnetron and the choke coils are sealed in a shield box so as to prevent the leakage of undesirable electromagnetic waves emitted from said cathode section. With such construction, the capacitor of the low pass filter must withstand the operating voltage of the magnetron, namely as high voltage as ten and odd kilovolts, resulting in the high cost of the capacitor and in consequence the magnetron device.

Another type of prior art magnetron device is provided with an L-C low pass filter utilizing a floating capacity and the inductance of an inductor composed of a plurality of series connected ferrite beads bored with two penetrating holes through which a pair of filament lead conductors are inserted. The L-C low pass filter of such magnetron, though producible at a low cost, is not fully effective to prevent the leakage of noise microwaves.

It is accordingly the object of this invention to provide a magnetron device using an inexpensive low pass filter capable of very effectively preventing the leakage of noise microwaves.

According to an aspect of this invention, there is provided a magnetron device, wherein a high frequency choking system is received in a shield box disposed on that side of the magnetron tube which faces a cathode stem; and said choking system is composed of a pair of choking members connected to a pair of filament lead conductors, each choking member being formed of at least one first choking element including a high frequency core of high intrinsic resistivity directly connected to a filament lead conductor and at least one second choking element including a low frequency core of low intrinsic resistivity connected to the first choking element.

This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawing, in which:

FIG. I is a plan view of a magnetron device according to an embodiment of this invention;

FIG. 2 is a side view of the magnetron device of FIG.

FIG. 3 is a plan view of a magnetron device according to a second embodiment of the invention, wherein a shield is disposed near that ofthe cores of each choking member which is disposed on a power source side;

FIG. 4 is a side view of the second embodiment of FIG. 3;

FIG. 5 is a plan view ofa magnetron device according to a third embodiment of the invention modified from FIG. I, wherein a plate shield member is interposed between the iirst choking elements and the second choking elements of a pair of choking members;

FIG. 6 is a plan view of a magnetron device according to a fourth embodiment of the invention modified from FIG. 3;

FIG. 7A is a schematic plan view of a magnetron device according to a fifth embodiment of the invention, wherein each choking member includes a plurality of second choking elements;

FIG. 7B is a schematic plan view ofa magnetron device according to a sixth embodiment of the invention, wherein a plate shield member is disposed between the first choking element and the adjacent second choking element of each choking member;

FIG. 8 is a plan view ofa magnetron device according to a seventh embodiment of the invention, wherein a choking system composes two series connected ferrite core beads;

FIG. 9 is a side view of the seventh embodiment of FIG. 8;

FIG. 10 is a plan view of a magnetron device according to an eighth embodiment of the invention, wherein a choking system is formed of a plurality of series connected ferrite core beads;

FIG. ll is a graph showing data of comparison between the noise characteristics of the prior art magnetron and that of the present magnetron, as obtained from the AGC voltage of a television receiver.

Referring to the first embodiment of FIGS. 1 and 2, a magnetron 11 is used, for example, in cooking food material by microwave energy emitted from an output antenna held in the closed oven chamber (not shown) of, for example, an electronic oven. The magnetron 11 is provided with a magnet I3 and radiator I4. The cathode bushing 15 of the magnetron 11 is provided with heater lead terminals or filament lead terminals 16a, 16b. A pair of choking members 17a, 17b are connected to these lead terminals 16a, 16b respectively. The choking member comprises a pair of choking elements l7a-l, I7a-2 composed of series connected coils 18a, 19a and cores 20a, 21a inserted thereinto. Similarly, the choking member 17b comprises a pair of choking elements l7b-l, l7b-2 composed of series connected coils 18b, 19b and cores 20b, 21b inserted thereinto. The cores 20a. 20b are formed of NiZn-base ferrite (manufactured, for example, by Tokyo Denki Kagaku under a commercial name Q,C") having a prominent permeability to high frequency and a high intrinsic resistivity of more than 1 Kfl-cm, for example 10 Kflcm at a room temperature. The cores 21a, 21b are made of MnZn-base ferrite (manufactured, for example, by Tokyo Denki Kagaku under a commercial name I-I;,S") having a prominent permeability to low frequency and a low intrinsic resistivity ofless than I00 .Q-cm, for example 30 (Tom at a room temperature. The choking members 17a, 17b and cathode bushing I5 are received in a shield box 22. The leads 23a, 23b of the choking members 17a, 1710 are connected to the terminals 25a, 25b through the insulation wall 24 formed at a part of the shield box 22.

Provision of the choking members 17a, 17b of the above-mentioned arrangement substantially prevents the leakage of objectionable noise microwaves of VHF and UHF bands emitted from the cathode bushing 15 during the operation of the magnetron ll, thereby 3,9 3 keeping a television receiving set practically free from the effect of such noise microwaves. where Where. therefore, noise microwaves are treated by the choking members 17a, 17b set at a mode capable of readily absorbing such noises, then the noise microwaves are prominently attenuated and least likely to leak to the outside. However, such mode is not realized if all the cores 20a, 20b, Zla, 21b of the choking mem bers 17a. 17!; are made of the same material. But only whre the cores 20a. 20b positioned near the cathode of the magnetron II are made of material having a higher intrinsic resistivity than the cores 21a, 21b facing the power supply terminals 25a, 25b, then can be attained the above-mentioned mode, in which the undesirable noise microwaves can be easily absorbed by the choking members 170, l7b, thereby substantially presenting the leakage of said noise microwaves.

According to a second embodiment of FIGS. 3 and 4, the choking member 17a comprises a choking element I7a-1 including a core 200 of high intrinsic resistivity and a choking element l7a-2 including a core 21a of low intrinsic resistivity. Similarly, the choking member l7b comprises a choking element l7b-l including a core b of high intrinsic resistivity and a choking element l7b-2 including a core 21b of low intrinsic resistivity. The choking element l7a-2 including the core 21a of low intrinsic resistivity and the choking element l7b-2 including the core 21!) of low intrinsic resistivity are respectively surrounded by shield cylinders 26a. 26b into which the corresponding insulation silicon tubes 27a, 27b are inserted. This arrangement enables objectionable noise microwaves emitted from the cathode bushing 15 to be effectively absorbed.

If the foregoing embodiments are further modified by providing a prescribed space between the cores 20a and 21a of different intrinsic resistivities, as well as between the cores 20b and 21b of different intrinsic resistivities or intcrposing, as shown in FIGS. 5 and 6, a metal shield plate 28 between the cores constituting said two groups so as to attain magnetic insulation therebetween, then noise microwaves can be more effectively absorbed.

Referring to the embodiments of FIGS. 7A and 78, a choking member 30 comprises a first choking element 33 including a core 330 of high intrinsic resistivity located near a cathode bushing 32 and a plurality of second choking elements 34, 35 respectively including cores 34a, 35a of low intrinsic resistivity. Another choking member 31 has the same arrangement. Each of these choking members 30, 31 is surrounded by a silicon tube 36. The outer surface of that part of the silicon tube 36 which faces the plural second choking elements 34, 35 is covered with an aluminium shield membrane 37.

If, as shown in FIGS. 7 and 8, each of the choking elements 30, 31 comprises a first choking element 33 including a core 33a of high intrinsic resistivity and disposed near the cathode bushing 32 and a plurality of second choking elements 34, 35 including cores 34a, 35a of low intrinsic resistivity connected in series to the first choking element 33, and the respective choking elements 33, 34, 35 are set at prescribed modes, then noise microwaves having a considerably broad band range can be effectively absorbed.

According to the embodiment of FIG. 78, a shield plate member 38 is further provided between the first choking element 33 and the adjacent second choking element 34.

Referring to the embodiment of FIGS. 8 and 9, the choking member comprises a ferrite core bead 40 of high intrinsic resistivity and a ferrite core bead 4] of low intrinsic resistivity which are respectively bored with two penetrating holes and aligned to each other in series. and a pair of heater or filament leads 42, 43 passing through said holes. In this case. the paired filament leads 42, 43 act as the choking coils described in the foregoing embodiment. These filament leads 42, 43 and ferrite core beads 40. 41 form choking members. Such choking member is of simple arrangement and can be made compact.

According to the embodiment of FIG. 10, the choking member comprises a plurality of groups of alternately connected ferrite core beads 40, 41, each being of the same type as described above. A pair of filament leads 42, 43 are inserted through the penetrating holes bored in said ferrite core beads. The arrangement of the choking member shown in FIG. 10 can absorb noise microwaves having a considerably broad band range.

Examination of the effect exerted by the noise microwaves emitted from an electronic oven equipped with a magnetron, for example. on a television receiving set can be conveniently carried out by measuring changes in the AGC voltage of said receiving set. FIG. ll graphically sets forth the data obtained from this test method. The curve 51 indicates changes in the AGC voltage of a television receiving set caused by noise mi crowaves emitted from a magnetron-type electronic oven omitting a filter. The curve 52 shows changes in the AGC voltage of a television receiving set caused by noise microwaves leaking from an electronic oven using a magnetron device according to the embodiment of FIGS. 1 and 2. The curve 53 denotes changes in said AGC voltage resulting from noise microwaves discharged from an electronic oven containing a magnetron device according to the embodiment of FIG. 7A. The curve 54 illustrates changes in the AGC voltage arising from noise microwaves emitted from an electronic oven provided with a magnetron device according to the embodiment of FIG. 78 wherein a shield plate 38 is provided between the first choking element 33 including the core 330 of high intrinsic resistivity and the second choking element 34 including the core 34a of low intrinsic resistivity. As apparent from FIG. 1 l a noise microwave-absorbing filter utilizing the choking member of this invention has a far higher filtering effect and is much more inexpensive than the prior art filter.

Each of said choking members may comprise at least one choking element formed of a ferrite core and a choking coil wound about said ferrite core; and at least one more choking element constituted by a ferrite core bead in which a lead conductor connected to said choking coil is received.

What is claimed is:

l. A magnetron device comprising a magnetron body; means for applying a magnetron field to the magnetron body; a cooling device fitted to the magnetron body; a shield box disposed on that side of the magnetron body which faces a cathode stem; and a noise microwave-absorbing filter received in the shield box, wherein the noise microwave-absorbing filter is composed of a pair of choking members respectively connected to heater lead conductors; each choking member is composed of at least one first choking element including a first ferrite core of high intrinsic resistivity connected to the heater lead conductor and at least one second choking element including a second ferrite core of low intrinsic resistivity connected in series to the first choking element.

2. A magnetron device according to claim 1, wherein the first ferrite core is made of a NiZn-base high frequency core. and the second ferrite core is formed of a MnZn-base low frequency core.

3. A magnetron device according to claim 1, wherein the paired choking members are used at a maximum ambient temperature of 150C 4. A magnetron device according to calim 1, wherein each of the paired choking members comprises the first choking element including a first coil wound about the first core and connected at one end to the heater lead conductor and the second choking element including a second coil wound about the second core and connected to the other end of the first coil of the first choking element,

5. A magnetron device according to claim 4, wherein the second choking element is surrounded by a shield member.

6. A magnetron device according to claim 5, wherein the shield member receives an insulation tube.

'7. A magnetron device according to claim 1, wherein each of the paired choking members includes a plurality of series connected second choking elements.

8. A magnetron device according to claim 1, wherein a shield plate member is provided between the first choking element and the adjacent second choking element.

9. A magnetron device comprising a magnetron body; means for applying a magnetic field to the magnetron body; a cooling device fitted to the magnetron body; a shield box disposed on that side of the magnetron body which faces a cathode stem; and a noise microwave-absorbing filter received in the shield box,

wherein the noise microwave-absorbing filter is composed of a pair of choking members respectively connected to a pair of heater lead conductors; each of the paired choking members is composed of a first choking element including a first coil connected at one end to the heater lead conductor and a first ferrite core of high intrinsic resistivity inserted into the first coil and a plurality of second choking elements including a plurality of second coils connected in series to the first coil of the first choking element and a plurality of second ferrite cores of low intrinsic resistivity inserted into the plural second coils; the first choking element and the plural second choking elements of each choking mem her are surrounded by a silicon tube; that part of the silicon tube which faccs the plural choking elements is enclosed in a shield cylinder; and a shield plate member is provided between the first choking member and the adjacent second choking member 10. A magnetron device comprising a magnetron body; means for applying a magnetic field to the magnetron body; a cooling device fitted to the magnetron body; a shield box disposed on that side of the magnetron body which faces a cathode stern; and a noise microwave-absorbing filter received in the shield box, wherein the noise microwave-absorbing filter includes at least one first ferrite core bead of high intrinsic resistivity bored with a pair of penetrating holes and disposed on that side of the magnetron body which faces the cathode stem; at least one second ferrite core bead of low intrinsic resistivity bored with a pair of penetrating holes and positioned adjacent to the first ferrite core bead; and a pair of conductors passing through the paired penetrating holes of the first and second ferrite core beads to be connected to a pair of heater leads fitted to the cathode stem of the magnetron body.

i i i UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3 922 12 DATED November 25, 1975 INVENTOR(S) Norio Tashiro It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Claim 1, line 2, please delete "magnetron field and insert therefor --magnetic field--.

Signal and Scaled this A nest:

RUTH C. MASON C. MARSHALL DANN Anemng Ofl'irer (ommr'ssr'nner uj'Parem: and Trademark: 

1. A MAGNETRON DEVICE COMPRISING A MAGNETRON BODY; MEANS FOR APPLYING A MAGNETRON FIELD TO THE MAGNETRON BODY; A COOLING DEVICE FITTED TO THE MAGNETRON BODY; A SHIELD BOX DISPOSED ON THAT SIDE OF THE MAGNETRON BODY WHICH FACES A CATHODE STEM; AND A NOISE MICROWAVE-ABSORBING FILTER RECEIVED IN THE SHIELD BOX, WHEREIN THE NOISE MICRONWAVE-ABSORBING FILTER IS COMPOSED OF A PAIR OF CHOKING MEMBERS RESPECTIVELY CONNECTED TO HEATER LEAD CONDUCTORS; EACH CHOKING MEMBER IS COMPOSED OF AT LEAST ONE FIRST CHOKING ELEMENT INCLUDING A FIRST FERRITE CORE OF HIGH INTRINSIC RESISTIVITY CONNECTED TO THE HEATER LEAD CONDUCTOR AND AT LEAST ONE SECOND CHOKING ELEMENT INCLUDING A SECOND FERRITE CORE OF LOW INTRINSIC RESISTIVITY CONNECTED IN SERIES TO THE FIRST CHOKING ELEMENT.
 2. A magnetron device according to claim 1, wherein the first ferrite core is made of a NiZn-base high frequency core, and the second ferrite core is formed of a MnZn-base low frequency core.
 3. A magnetron device according to claim 1, wherein the paired choking members are used at a maximum ambient temperature of 150*C.
 4. A magnetron device according to calIm 1, wherein each of the paired choking members comprises the first choking element including a first coil wound about the first core and connected at one end to the heater lead conductor and the second choking element including a second coil wound about the second core and connected to the other end of the first coil of the first choking element.
 5. A magnetron device according to claim 4, wherein the second choking element is surrounded by a shield member.
 6. A magnetron device according to claim 5, wherein the shield member receives an insulation tube.
 7. A magnetron device according to claim 1, wherein each of the paired choking members includes a plurality of series connected second choking elements.
 8. A magnetron device according to claim 1, wherein a shield plate member is provided between the first choking element and the adjacent second choking element.
 9. A magnetron device comprising a magnetron body; means for applying a magnetic field to the magnetron body; a cooling device fitted to the magnetron body; a shield box disposed on that side of the magnetron body which faces a cathode stem; and a noise microwave-absorbing filter received in the shield box, wherein the noise microwave-absorbing filter is composed of a pair of choking members respectively connected to a pair of heater lead conductors; each of the paired choking members is composed of a first choking element including a first coil connected at one end to the heater lead conductor and a first ferrite core of high intrinsic resistivity inserted into the first coil and a plurality of second choking elements including a plurality of second coils connected in series to the first coil of the first choking element and a plurality of second ferrite cores of low intrinsic resistivity inserted into the plural second coils; the first choking element and the plural second choking elements of each choking member are surrounded by a silicon tube; that part of the silicon tube which faces the plural choking elements is enclosed in a shield cylinder; and a shield plate member is provided between the first choking member and the adjacent second choking member.
 10. A magnetron device comprising a magnetron body; means for applying a magnetic field to the magnetron body; a cooling device fitted to the magnetron body; a shield box disposed on that side of the magnetron body which faces a cathode stem; and a noise microwave-absorbing filter received in the shield box, wherein the noise microwave-absorbing filter includes at least one first ferrite core bead of high intrinsic resistivity bored with a pair of penetrating holes and disposed on that side of the magnetron body which faces the cathode stem; at least one second ferrite core bead of low intrinsic resistivity bored with a pair of penetrating holes and positioned adjacent to the first ferrite core bead; and a pair of conductors passing through the paired penetrating holes of the first and second ferrite core beads to be connected to a pair of heater leads fitted to the cathode stem of the magnetron body. 